Neutrally buoyant vertical underwater cable

ABSTRACT

A cable for vertical suspension underwater and essentially neutrally buoyant at all depths has a core of material of slightly less specific gravity than the water and a surrounding sleeve element of higher specific gravity than the water, the weight and/or the water/displacing relation of said core and sleeve elements being adjustable to provide neutral buoyancy of the cable at its various depths when vertically suspended under force of a weight.

United States Patent Edward M. Herrmann 105 Round Bay Road, Severna Park, Md. 21 146 Apr. 25, 1969 Apr. 6, 1971 Inventor Appl. No Filed Patented NEUTRALLY BUOYANT VERTICAL UNDERWATER CABLE 7 Claims, 3 Drawing Figs.

US. Cl 174/101.5, 9/8,174/110,174/113 Int. Cl H01b 7/12 FieldotSearch 174/10l.5,

[56] References Cited UNITED STATES PATENTS 2,279,625 4/1942 Lancaster 174/42 2,584,027 1/1952 Kendrick 174/1 13.3X

3,017,934 l/l962 Rhodes 166/.5 3,443,020 5/1969 Loshigian 174/101 .5 3,454,783 7/1969 Hunt 174/110X Primary Examiner-E. A. Goldberg Attorneys-L. A. Miller, Q. E. Hodges and A. Sopp ABSTRACT: A cable for vertical suspension underwater and essentially neutrally buoyant at all depths has a core of material of slightly less specific gravity than the water and a surrounding sleeve element of higher specific gravity than the water, the weight and/or the water/displacing relation of said core and sleeve elements being adjustable to provide neutral buoyancy of the cable at its various depths when vertically suspended under force of a weight.

NEUTRALLY BUOYANT VERTICAL UNDERWATER CABLE The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Hoisting winches are subject to heavy loads when the raised or lowered cable is of greater weight than the water it displaces. If the cable is much lighter than the water it displaces, then heavy dead weights must be used to submerge the cable.

Cables having neutrally buoyant portions are known in the art, but are of very complex construction and are unsuitable for vertical orientation to deep depths in sea water SUMMARY A cable according to the present invention is comprised of essentially two elements respectively of greater and less specific gravity than the sea water displaced thereby. The two elements are arranged so that their combined specific gravity at any depth is that of the locally displaced sea water. The resulting neutrally buoyant cable may hang vertically by virtue of its CG being slightly lowered by means of the weight of a suspended or towed object such as a sonar array, lifting hook, etc.

One of the two elements employed may be acore of material such as polyethylene or polypropylene having a specific gravity less than the displaced water and the other element an outer helix wound around the core and formed of conductive material sheathed in insulation and having a specific gravity greater than the displaced water. The pitch of the helix (i.e. space between windings) is increased as depth increases because the specific gravity of sea water and of the core material increases with depth. Other configurations of the two material elements of the cable may be employed so long as the composite specific gravity of the cable at any depth is that of the surrounding water.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is now made to the drawings in which like numerals represent like parts and in which:

FIG. 1 is a view of a cable according to the invention shown suspended essentially vertically;

FIGS. 2 and 3 are views in perspective of cable arrangements according to the invention.

DETAILED DESCRIPTION AND OPERATION In FIG. 1 there is shown a watercraft 11 having a pulley 13 from which there is suspended into sea water 15 a cable 17 constructed in accordance with the principles of the invention. As shown in FIG. 2, the cable 17 is composed of a continuous cylindrical-shaped core 19 of polyethylene, polypropylene, or any other suitable relatively noncompressible material of less specific gravity than the water 15 it displaces and being sufficiently flexible as to enable its being winched. Specific gravity is defined as the ratio between the density of a substance at a given temperature and the density of some substance assumed as standard. For liquids the standard assumed is either the density of distilled water at 4 C. or the density of distilled water at 60 F. The cable has wound therearound in the form of a helix an insulated conductor 21 of specific gravity greater than the water 15 it displaces. Conductor 21 may be attached to the core 19 in any suitable wellknown manner, as by welding, bonding, stapling, etc.

The sea water pressure is greater at progressively deeper portions of the suspended cable 17. Under higher pressure the radial dimension of the core 19 decreases with depth. That is, the core 19 is compressed, increasing its density and thus, its

specific gravity, and decreasing its buoyancy in the displaced water 15. Therefore, at deeper depths, the heavier conductive material 21 has its windings progressively further apart as indicated at legended positions a, b, and 0, so that the composite specific gravity of the cable thereat is the same as that of the ambient water it displaces.

The arrangement of FIG. 3 is alternative to that of FIG. 2 and employs a central core of flexible materials 23 of less specific gravity than water and sleeve material 25 of more specific gravity than water. The sleeve 25 is composed of flexible rubber hose 27 having longitudinal strength members 29 embedded therein which may act as electrical conductors. Members 29 may be of any suitable material such as titanium, plastic or glass fiber, steel, etc. Of course,should it be desired that members 29 act as conductors, conductive materials should be employed. Variations in specific gravity of the core and sleeve materials due to high sea water pressure at great depths may be compensated for in accordance with the principles herein by increasing the ratio of core to sleeve material at progressively deeper transverse cross sections of the cable.

The ratio of specific gravity of the component elements of the cable can be determined by experiment or can be calculated beforehand. The general relation is that the water displaced per unit length by the vertically suspended cable (i.e. its core and sleeve conductor elements together) is equal to the total weight of the core and surrounding sleeve conductor in air. Mathematically,

where R is the outside radius of the sleeve and conductive material of higher specific gravity than the displaced water;

r is the radius of the core material of lesser specific gravity than the displaced water;

d is the density or specific gravity of the core material;

d, is the density or specific gravity of the conductive material;

and R represents the weight of the water displaced by the cable. H v

If the displaced water and conductive material are considered as essentially incompressible, the specific gravity of the core material such as polyethylene may be 0.91 near the water surface and about 0.95 at, say, 10,000 feet, increasing about 0.01 for each 2,500 feet of depth. Equation (1) may then be solved for various depths to render the appropriate dimension of the core element given the specific gravities and R, or, the appropriate weight per unit length of the conductive material, given r.

In the case where both the core and sleeve are made of material compressible in proportion to depth of suspension, the ratio of more dense sleeve to the less dense, buoyant core material may be determined in the laboratory, depending upon the materials employed. For example, with a core of polypropylene surrounded by a rubber sleeve, both materials will compress radially with depth. Environmental testing tanks providing very high pressures in excess of 20,000 p.s.i. are known in the art. Cable sections may be placed in the test tank, and the extent of reduction in their radial dimensions due to compression observed. The observed reduction in radius at various particular pressures representing sea water depths enables calculation of the proper transverse cross section of the cable at each measured pressure (depth) so that the same water displacement is afforded by each cable section regardless of depth, thereby insuring essentially neutral buoyancy at all depths.

While in accordance with the present invenfin a vertically oriented cable of neutral buoyancy is related to a predetermined depth at which use of the cable is intended, a cable for use at such depth may be used at other depths with a slight sacrifice in neutral buoyancy.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that the invention may be practiced otherwise than as specifically described.

I claim 1. A cable for vertical orientation in sea water and to which a load may be attached, said cable being neutrally buoyant for substantially its entire length to a predetermined depth in the sea water and comprising:

first elongated body means composed of material having flexibility for winding on a winch, said material having a specific gravity less than the specific gravity of water; second elongated flexible body means surrounding said first body means for substantially the entire cable length; said second body means being of essentially constant specific gravity greater than the specific gravity of water; said second body means being disposed along said first body means in decreasing amount by weight in air per unit length of the cable in proportion to the sea water depth of the cable; and whereby the composite specific gravity of the cable when in use at all depths is essentially that of water. 2. The cable of claim 1 wherein one of said body means further includes electrically conductive means.

3. The cable of claim 1 wherein said second elongated body means is essentially incompressible and comprises a helical winding the pitch of which increases in relation to the depth of said cable in said sea water.

4. The cable of claim 1 wherein said first elongated body means comprises a continuous cylindrical body means and said second body means comprises sleeve means surrounding said cylindrical body means, the ratio of said cylindrical body means material to said sleeve means material in transverse cross section increasing with greater depthto thereby provide a specific gravity of essentiallythat of water for the cable at all depths.

5. The cable of claim 4 wherein said sleeve means comprises a rubber sleeve having longitudinal strength members therein.

6. The cable of claim 5 whereinsaid longitudinal strength member comprise electrically conductive material.

7. The cable of claim 3 wherein said helical winding comprises insulated electrically conductive material. 

1. A cable for vertical orientation in sea water and to which a load may be attached, said cable being neutrally buoyant for substantially its entire length to a predetermined depth in the sea water and comprising: first elongated body means composed of material having flexibility for winding on a winch, said material having a specific gravity less than the specific gravity of water; second elongated flexible body means surrounding said first body means for substantially the entire cable length; said second body means being of essentially constant specific gravity greater than the specific gravity of water; said second body means being disposed along said first body means in decreasing amount by weight in air per unit length of the cable in proportion to the sea water depth of the cable; and whereby the composite specific gravity of the cable when in use at all depths is essentially that of water.
 2. The cable of claim 1 wherein one of said body means further includes electrically conductive means.
 3. The cable of claim 1 wherein said second elongated body means is essentially incompressible and comprises a helical winding the pitch of which increases in relation to the depth of said cable in said sea water.
 4. The cable of claim 1 wherein said first elongated body means comprises a continuous cylindrical body means and said second body means comprises sleeve means surrounding said cylindrical body means, the ratio of said cylindrical body means material to said sleeve means material in transverse cross section increasing with greater depth to thereby provide a specific gravity of essentially that of water for the cable at all depths.
 5. The cable of claim 4 wherein said sleeve means comprises a rubber sleeve having longitudinal strength members therein.
 6. The cable of claim 5 wherein said longitudinal strength member comprise electrically conductive material.
 7. The cable of claim 3 wherein said helical winding comprises insulated electrically conductive material. 